ScheduledExecutorService

Class Overview

An ExecutorService that can schedule commands to run after a given delay, or to execute periodically.

The schedule methods create tasks with various delays and return a task object that can be used to cancel or check execution. The scheduleAtFixedRate and scheduleWithFixedDelay methods create and execute tasks that run periodically until cancelled.

Commands submitted using the execute(Runnable) and ExecutorService submit methods are scheduled with a requested delay of zero. Zero and negative delays (but not periods) are also allowed in schedule methods, and are treated as requests for immediate execution.

All schedule methods accept relative delays and periods as arguments, not absolute times or dates. It is a simple matter to transform an absolute time represented as a Date to the required form. For example, to schedule at a certain future date, you can use: schedule(task, date.getTime() - System.currentTimeMillis(), TimeUnit.MILLISECONDS). Beware however that expiration of a relative delay need not coincide with the current Date at which the task is enabled due to network time synchronization protocols, clock drift, or other factors. The Executors class provides convenient factory methods for the ScheduledExecutorService implementations provided in this package.

Usage Example

 import static java.util.concurrent.TimeUnit;
 class BeeperControl {
    private final ScheduledExecutorService scheduler = 
       Executors.newScheduledThreadPool(1);

    public void beepForAnHour() {
        final Runnable beeper = new Runnable() {
                public void run() { System.out.println("beep"); }
            };
        final ScheduledFuture<?> beeperHandle = 
            scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
        scheduler.schedule(new Runnable() {
                public void run() { beeperHandle.cancel(true); }
            }, 60 * 60, SECONDS);
    }
 }
 

Summary

[Expand] Inherited Methods
From interface java.util.concurrent.Executor abstract void execute(Runnable command) Executes the given command at some time in the future.
From interface java.util.concurrent.ExecutorService abstract boolean awaitTermination(long timeout, TimeUnit unit) Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first. abstract <T> List<Future<T>> invokeAll(Collection<Callable<T>> tasks, long timeout, TimeUnit unit) Executes the given tasks, returning their results when all complete or the timeout expires, whichever happens first. abstract <T> List<Future<T>> invokeAll(Collection<Callable<T>> tasks) Executes the given tasks, returning their results when all complete. abstract <T> T invokeAny(Collection<Callable<T>> tasks, long timeout, TimeUnit unit) Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses. abstract <T> T invokeAny(Collection<Callable<T>> tasks) Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do. abstract boolean isShutdown() Returns true if this executor has been shut down. abstract boolean isTerminated() Returns true if all tasks have completed following shut down. abstract void shutdown() Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. abstract List<Runnable> shutdownNow() Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. abstract Future<?> submit(Runnable task) Submits a Runnable task for execution and returns a Future representing that task. abstract <T> Future<T> submit(Runnable task, T result) Submits a Runnable task for execution and returns a Future representing that task that will upon completion return the given result abstract <T> Future<T> submit(Callable<T> task) Submits a value-returning task for execution and returns a Future representing the pending results of the task.